The carbapenem compounds which have been developed and commercialized are poor in absorbability from the digestive tract and therefore, they are clinically used only in a form of injection, mainly intravenous injection. However, in the clinical field, it is desirable to select several administration routes from the viewpoint of circumstances or wishes of a patient, a therapeutic object, etc. Especially, oral administration of an antibacterial agent is easy and convenient for administration to a patient in comparison with injection. In view of the care of a patient at home, oral administration of the antibacterial agent is more convenient and the clinical usability is extremely high. It has been strongly desired in the clinical field to develop a carbapenem compound which has a potent antibacterial activity especially against penicillin-resistant Streptococcus pneumoniae (PRSP) which has been isolated at an elevated frequency in recent years and thus causes a serious clinical problem, and Haemophilus influenzae which has acquired resistance against the existing β-lactam antibiotics over a wide scope due to penicillin-binding protein (PBP) mutations such as β-lactamase non-producing ampicillin-resistant (BLNAR) Haemophilus influenzae, and is rich in safety and is orally administrable. However none of such agents has been put on the market. Tricyclic carbapenem compounds which have been studied and developed until now are disclosed for example, in WO92/03437. These compounds have a characteristic structure in a side chain having a ring which is fused via C—C bond and they are modified to a prodrug thereof for increase of oral absorbability, but their safety in the clinical test is not reported. Besides, there are several known 1β methylcarbapenem compounds (Japanese patent publication 2-49783, Japanese patent publication 8-53453, Japanese patent publication 4-279588, Japanese patent publication 2-223587, WO98/34936, WO99/57121, Antimicrobial Agents and Chemotherapy, Mar. 1999, p460–464). All of them have a structural property having 1β-methyl group and a side chain via sulfide bond which are the said to contribute to an increase of chemical stability and in vivo (biological) stability, and are modified to a prodrug of them for increase of oral absorbability. Especially, the clinical trial was carried out on compounds disclosed in Japanese patent publication 2-49783 and Japanese patent publication 8-53453, but the safety of them and so on have been not clear.
On the other hand, carbapenem compounds having an aryl ring via C—C bond as a side chain structure were known since 1980s (U.S. Pat. No. 4,775,669, U.S. Pat. No. 5,258,509, Tetrahedron, 1983, Vol. 39, p2531–2549, Journal of Medicinal Chemistry, 1987, Vol. 30, p871–880). Although there are many other reports on these compounds, these reports are concerned only to studies and developments on injections thereof, but not to studies for oral application thereof.